4. At low pH it precipitates iron
quantitatively
At higher pH it forms insoluble complexes
with all other polyvalent cations.
Some of the important physiological
function-of phytic acid include storage
of phosphorus, high-energy phosphate
groups, am; cations, and protection of
seeds against oxidative damage during
storage.
5. The antioxidant functions of phytic acid have been
described by Graf and Eaton
Phytic acid has a relatively high binding affinity for iron and
is a potent inhibitor of iron-mediated hydroxyl radical
formation.
In the absence of phytate, Fe + is completely insoluble at
neutral or higher pH due to the formation of large
polynuclear iron hydroxide complexes.
High concentrations of phytic acid solubilize iron in the form
of Fe(III) 1-phytate, whereas low concentration precipitate
iron as Fe(III)3- and Fe(III)4-phytate complexes.
Chelating of iron by phytic acid prevents the formation of
polynuclear aggregates even at iron concentrations as low
as 6 nM.
The six coordination sites of trivalent iron are occupied by
water and hydroxide ions in aqueous solutions.
6. Most chelating agent displace five of these ligands and
form a pentadentate chelate with H2O occupying the
sixth coordination site.
Phytic acid, however, is unique in occupying six
coordination sites and displacing all of the coordination
water in the Fe(III)complex.
Iron-catalyzed formation of hydroxyl radical requires the
availability of at least one reactive iron coordination site
as well as iron solubility.
Phytic acid preserves the solubility and makes the metal
totally enactive.
In molar phytate-to-iron ratios of 0.25 and above, the
supcroxidc-driven generation c: hydroxyl radical is
completely blocked.
7. Phytic acid appears to be one of the most effective agents
for the inhibition of iron-mediated lipid oxidation in foot
products.
In meat products, it presumably removes myoglobin-derived
iron froivi negatively charged phospholipids and prevents
their autoxidation and off-flavor formation.
Phytic acid substantially inhibits oxygen uptake,
malondialdehyde formation, and warmed-over flavor
development in cooked minced chicken breasts stored in
sealed oxygen-impermeable containers at 4°C.
In a soybean oil-in-water emulsion system, the oxidation was
significantly decreased by the addition of 1M phytic acid.
Phytic acid also significantly reduces the iron-catalyzed
oxidation and partially inhibits the copper-mediated
oxidation of ascorbic acid in model systems
8. Phospholipids or phosphatides occur in all living organisms
and make up l-2% of many crude oils and animal fats.
The term lecithin was initially used for crude fractions of
phospholipids obtained from vegetable oils or fats.
At present it is used to refer to phosphatidylcholine (l,2-
diacylglycero-3-phosphorylcholinc).
It is also used to describe soybean lecithin, which is
composed of soybean-phosphatides and soybean oil.
Chemically, phosphatidylcholine consists of a glyceride in
which two of the hydroxyl groups are esterified with fatty
acids and the third is verified with a phosphoric acid that
in turn is bound to a molecule of choline. In
phosphatidylethanolamine, the choline is replaced by
ethanolamine.
The commercial source of lecithin is mainly soybeans.
9.
10. Some of the parameters that characterize commercial
lecithin are acetone-insoluble matter, acid value,
moisture content, hexane-insoluble matter, color,
consistency, and clarity.
Commercial lecithin insists of about 66% phospholipids, the
other major components being the glycerides.
Lecithin is classified as plastic or fluid according to its viscosity.
Each of these is further classified into natural, bleached, or
unbleached grades based on color.
Only the unbleached grades are permitted as food additives.
Commercial lecithin can also be produced as a powder by
alcohol or acetone extractions.
It is soluble in oils and is hydrated in water with the formation
of an emulsion.
11. The phospholipids function synergistically with primary
antioxidants, especially the tocopherols, in stabilizing various
fats and oils.
Lecithin also functions as a carrier for antioxidants such as PG
in commercial mixtures.
Commercial mixtures containing lecithin, a-tocopherol, and
ascorblypalmitate or ascorbic acid are available.
In such mixtures, ascorbic acid regenerates tocopherol
mediated by lecithin.
However, the mechanism is not understood.
The various applications of the synergistic mixtures have been
described here under the food applications of toeopherols.
